Micro structure stent configurations

ABSTRACT

Fine structure stents physiologically acceptable to the body.

BACKGROUND OF THE INVENTION

This invention relates to medical stents. Medical stents are well knowfor use in opening and reinforcing the interior wall of blood vesselsand other body conduits.

Stents are generally tubular in configuration and radially expandable.They may be of the self-expanding type or they may be mechanicallyexpandable with an outward pressure applied to the stent. Typically, thelater type stents are expanded by means of an interiorly positionedballoon. Stents may be made of various materials such as plastic ormetal. Presently, metal is the material of choice.

This invention is specifically concerned with stents in the form of aclosed cylinder which is made up of a plurality of struts, the strutsbeing deformed either permanently or otherwise upon expansion of thestent.

To-date, stents, particularly coronary stents, have been made up ofelements that are relatively large and of the following order:

strut width .004 inches-.008 inches strut thickness .002 inches-.007inches largest dimension of opening between struts .100 inches-.200inches

These dimensions and all other dimensions referred to herein after referto the stent in its expanded state.

The basic idea behind the present invention is to provide a stent offine structure (micro structure) that provides adequate vessel supportbut the openings therein are so small that the stent creates minimaldisruption of the vessel surface and is so fine that it is for allpractical purposes “invisible” to the body in which it is implanted andto the body constituents such as blood flow.

An analogous example is a window screen, the idea being to provide ascreen (stent) to support a vessel but which is from the stand point ofthe various physiological aspects of the body so fine as to beeffectively “invisible” and for all practical purposes can then be saidto be considered by the body as being nonexistent.

There does exist in the art one example of an ultra thin micro porousnickel titanium foil which is rolled in the fashion of a jelly roll toprovide a self-expanding stent. Self-expansion is provided by thenatural unrolling tendency of the tightly wound stent following itsimplantation. However, this type of stent has not been widely acceptableand differs from the stents of the present invention in that no strutdeformation occurs with respect to the elements making up the foil orscreen of the ultra thin micro porous jelly roll type stent.Cardiovascular Dynamics, Inc., has published material concerning the“jelly roll” stent.

BRIEF SUMMARY OF THE INVENTION

In contrast to the above-identified prior art, this invention providesstents of closed cylindrical construction in which expansion isaccompanied by deformation of the strut structure making up the body ofthe stent. As already pointed out, the term deformation is meant toinclude other deformation in addition to permanent deformation as usedin the metallurgical sense. In accordance with this invention a suitablemicro structure design can be obtained by dimensionally constructing astent having a reduction ratio as compared to current coronary stents of4:1 to 10:1. Note with reference to ratio reduction—current dimensionsare thereby reduced by a factor of about 4-10.

Even more specifically, micro structure stents in accordance with thepresent invention will preferably have about the following dimensions:

strut width 0.00025-0.002 inches strut thickness 0.00025-0.004 inchesmaximum PIN opening 0.002-0.020 inches diameter

(current stent designs typically have a maximum PIN opening of around0.025 inches to 0.050 inches in diameter).

The term “maximum PIN opening” is used herein to describe micro openingsin which the dimensions specify the largest which can be passed throughthe cell opening. This applies as noted above to the expanded stentconfiguration. Typically, as a stent is expanded to larger diameters,the opening becomes larger. It is believed that using a maximum PINopening specification that the concept of the present invention may bemore readily applicable to stents of either open or closed cellgeometries.

The preferred stents having a micro structure in accordance with thepresent invention will also have a wall thickness of up to about 0.004inches, which is not required according to the invention, but providesadequate radiopacity and handling characteristics in the stentstructure.

In addition to directly forming a micro structure in the wall of astent, this invention may be accomplished by providing a stent within astent wherein both stents, even though having larger openings than wouldbe characterized as providing micro structure, may in fact provide microstructure by control of the registration of the openings in the stentsas is more fully described below.

The stent within a stent combination leads to other embodiments of theinvention which are also described more fully below.

As with any stent design, many different designs are possible withrespect to features such as flexibility, etc. The geometries which areshown hereinbelow are included only for illustrative purposes.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a schematic fragment showing a micro structure stent of theinvention;

FIGS. 2 and 3 are schematic showings of a stent within a stent accordingto this invention;

FIG. 4 is a schematic showing of a section of a stent made up ofserpentine annular rings, the stent being bent;

FIG. 5 is a schematic showing of a stent similar to that of FIG. 4 butincluding an inner stent arranged according to this invention;

FIG. 6 is a schematic showing of a stent within a stent arrangedaccording to this invention;

FIG. 7 is a schematic showing of three stents arranged within each otheraccording to this invention, and

FIGS. 8-10 are schematic showings of another embodiment of the inventionfor providing multiple layer arrangements in a stent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention, in contrast to the prior art jelly roll structure,suggests that micro porous stents should be provided which have adeformable structure. Generally, this is meant that the deformablestruts of both self-expanding and mechanically-expandable stents alreadyknown in the art should be provided with micro porous structure. Thefabrication of such stents is typically from flat sheet which is rolledthen welded into a cylinder or from tubular stock.

A first way involves simply making the struts and the openings of thestent extremely small. Such a stent would be comprised of a plurality ofinterconnected deformable struts arranged with respect to each other toprovide a micro structure which facilitates support with a minimaldisruption in the vessel of a body, the micro structure beingcharacterized, after expansion, by about the following dimensions orsmaller.

strut width 0.00025-0.002 inches strut thickness 0.00025-0.004 inchesmaximum PIN opening 0.002-0.20 inches

Having reference to FIG. 1, there is shown in fragment a portion of astent 10 of closed cell geometry in schematic form. This stent could betaken to be formed of wire or wires 12 into a cylindrical configurationto form the stent 10. On the other hand, the struts formed by wire 12could also be manufactured by laser cutting struts 12 from tubular stockof an appropriate diameter.

A second way to achieve micro structure in a stent involves thecombination of one stent within another stent (slidably interfitted) inwhich the openings in the stents are mismatched or out of registerrelative to each other to provide an overall opening which is smallerthan either of any of the two registered openings. That is, the openingsdo not exactly correspond with each other and are not exactly alignedwith respect to each other. In such a situation each of the stents mayhave openings over a wide range of sizes which may or may not beindividually micro porous but together in registration provide microporous openings. However, when one stent is placed within the other andthe openings are positioned out of alignment with respect to each otherit can be seen that smaller openings through the combined stents can beachieved and can become micro porous even when the original openings arenot. Such a structure is shown in FIGS. 2 and 3 in which an aperturedstent 10 a is being slidably interfitted with an apertured stent 10 b.As can be seen in FIG. 3 when the two stents are completely combined,openings 12 a in stent 10 a when out of register with openings 12 b instent 10 b will provide openings 12 c of markedly smaller size thaneither of the openings 12 a or 12 b.

Such a combination may even include a third stent within the secondstent and so forth. Each stent in such a case would be fabricatedindependently following which the stents would be slidably interfittedone into the other to provide the overall combination.

The combined stents if tightly fit together would not necessarilyrequire any sort of fastening means. However, the stents may be joinedas by welding or by the use of adhesives. If adhesives are used, theadhesives could be biodegradable or even contain a drug elutingmaterial.

The primary purpose of using the second approach for achieving microstructure is based on the fact that it is easier to make fine holesthrough thin metal than through thick metal. Of course, for flexibilityconsiderations, each interfitted stent will preferably be as thin aspossible.

This concept of a stent within a stent has other ramifications as well.By fabricating each stent individually, one can achieve finer detailthan if thicker material is used. A limiting factor in most fabricationprocesses is depth to width ratio. With a thin working layer the levelof detail can be much finer.

Thus, even if one does not wish to fabricate a micro porous stent it maybe advantageous to utilize the stent within a stent concept to providestents which, although registered with each other in so far as theopenings therein are concerned, would provide a combination having afiner level of detail in the opening configuration.

Thus, the concept of a stent within a stent, when viewed broadly, wouldnot necessarily be limited to micro structure stents or to deformablestents but rather would be applicable broadly to stents in which it isdesired to obtain finer detail in the configuration of the patternmaking up the openings within the stent. This in addition to the primarypurpose of the subject invention in which the combination of multiplelayers, i.e., a stent within a stent to achieve stent strength and tocreate micro porous openings due to mismatch or lack of registration ofthe cell openings in each layer.

Presently, physicians sometimes implant a first stent and then implant asecond stent within the first stent. An embodiment of this inventioncontemplates a further development of this practice by providing a stentwithin a stent combination already for implant. Thus the two stents maybe implanted simultaneously. Several advantages are attendant with sucha combination.

The prior practice of implanting first one stent followed by theimplantation of a second stent within the first stent makes use ofpresently available stents of ordinary wall thickness. Such an implantedstent within a stent results in a relatively thick wall structure whichis detrimental to flexibility and also to flow dynamics within thevessel.

By providing a combination stent within a stent prior to implantation,one may combine stents purposely made of less than ordinary wallthickness to achieve thinner overall stent structure which will exhibitimproved overall performance such as:

Uniform vessel coverage

less gapping

small cell openings

improved flexibility

layers can move relative to each other

customized strength provided by adding or subtracting layers of stent.

For example, referring now to FIG. 4, a schematic showing of a wellknown type of stent configuration, generally indicated at 20, made up ofa series of serpentine annular rings 22 is shown. As can be seen in FIG.4, when the stent is bent to accommodate vessel curvature, gaps 24enlarge.

Referring now to FIG. 5, a similar stent 20 is shown having the standardannular serpentine rings 22. However, included within the stent is asimilar stent 26 arranged such that its rings 28 bridge the gaps 24 ofthe external stent 20 upon flexing or bending.

Customized stent strength may be accomplished by adding or subtractingstent layers. For example, refer to FIG. 6 which schematically shows astent 40 partially within a stent 42. High strength is provided atregion 44 where the two stents overlap and relatively low strength isprovided at regions 46 where there is but a single stent structure. Suchan arrangement provides a stent with soft ends.

Referring now to FIG. 7, a triple stent 40 within a stent 42 within astent 43 is shown to provide three layers in region 50, two layers inregions 52 and a single layer in regions 54, thus providing threeregions of different relative strength. Various other arrangements areavailable.

Lastly, variations in layers may be accomplished by rolling up agenerally triangular shaped piece of metal sheet 60 shown in FIG. 8???to form a cylinder 62 indicated in FIG. 9 which has in fact regions ofvarious layers as shown in FIG. 10. In FIG. 10 it can be seen that, whenrolled up, sheet 60 provides a cylindrical stent structure 64 havingmore layers in the mid regions 66 and successively fewer layers inregions 68 and even fewer in region 70.

The above examples and disclosure are intended to be illustrative andnot exhaustive. These examples and description will suggest anyvariations and alternatives to one of ordinary skill in the art. Allsuch alternatives and variations are intended to be included within thescope of the attached claims. Those familiar with the art may recognizeother equivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A stent of closed cylindrical constructioncomprised of a plurality of interconnected, deformable struts arrangedwith respect to each other to provide a micro structure whichfacilitates support with minimal disruption in a vessel or other bodyconduit, the micro structure being characterized, after expansion, byabout the following dimensions: strut width 0.00025″-0.002″ strutthickness 0.00025″-0.004″ maximum PIN opening  0.002″-0.020″.


2. The stent of claim 1 comprised of at least two stent bodies combinedone within the other.
 3. The stent of claim 2 in which the bodies arecombined so as to present the openings therein out of register withrespect to one another.
 4. The stent of claim 2 wherein the openings arein register with respect to each other.
 5. The stent of claim 2 wherein,a first stent body positioned internally of a second stent body forsimultaneous implantation.
 6. The stent of claim 5 wherein the firststent body is only partially within the second stunt body.
 7. The stentof claim 5 wherein both of the stent bodies are of the type including aplurality of annular segments.
 8. The stent claim 7 wherein the firststent body is arranged within the second stent body such that itsannular segments bridge gaps between the annular segments of the secondstent body.
 9. A stent comprised of a closed cylindrical body havingopenings therin, the openings, upon expansion of the stent, beingcharacterized by about the following dimensions: strut width0.00025″-0.002″ strut thickness 0.00025″-0.004″ maximum PIN opening 0.002″-0.020″.


10. The stent of claim 9 comprised of at least two stent bodies combinedone within the other.
 11. The stent of claim 9 in which the bodies arecombined so as to present the openings therein out of register withrespect to one another.
 12. The stent of claim 9 wherein the openingsare in register with respect to each other.
 13. A stent of closedcylindrial construction comprised of a plurality of interconnected,deformable struts arranged with respect to each other to provide a microstructure, the micro structure having a plurality of openings therein,the micro structure constructed and arranged to provide support to avessel or other body conduit while minimally interfering therewith,wherein upon expansion of the stent, the opening are characterized byhaving a maximum opening of 0.020″.
 14. The stent of claim 13 comprisedof at least two stent bodies combined one within the other.
 15. Thestent of claim 14 in which the bodies are combined so as to present theopenings therein out of register with respect to one another.
 16. Thestent of claim 14 wherein the openings are in register with respect toeach other.
 17. The stent of claim 13 wherein the struts having apredetermined width between approximately 0.00025″-0.002″.
 18. The stentof claim 17 comprised of at least two stent bodies combined one withinthe other.
 19. The stent of claim 17 in which the bodies are combined soas to present the openings therein out of register with respect to oneanother.
 20. The stent of claim 17 wherein the openings are in registerwith respect to each other.
 21. The stent of claim 13 wherein the strutshaving a predetermined thickness between approximately 0.00025″-0.004″.22. In combination, a first stent positioned internally of a secondstent for simultaneous implantation, the first and second stentcomprising a plurality of deformable struts arranged with respect toeach other to provide a micro structure, the micro structure having aplurality of openings therein, the micro structure constructed andarranged to provide support to a vessel or other body conduit whileminimally interfering therewith, wherein upon expansion of the stent,the openings are characterized by having a maximum opening of 0.020″.23. The combination of claim 22 wherein, the struts having apredetermined width between approximately 0.00025″-0.002″.
 24. Thecombination of claim 22 wherein, the struts having a predeterminedthickness between approximately 0.00025″-0.004″.